If it were me, when confronting him, I would have told him how gross that is to buy used panties from strangers on the internet. I mean that's just sick! If it were me, I would have broken up with him then and there for being so gross. Whether or not he actually bought them is irrelevant, the fact that he actually posted about it means he was thinking about it and a normal guy wouldn't do something like that, even if he didn't actually buy any. Really, how can you even look at the guy knowing this about him? Forget about the possible cheating thing, I'd ditch him for being a deviant.